Methodologies for non-destructive quantification of thermal barrier coating temperatures on service run parts

ABSTRACT

Methodologies for non-destructively inspecting and characterizing micro-structural features in a thermal barrier coating (TBC) on a component, wherein the micro-structural features define pores and cracks, if any, in the TBC. The micro-structural features having characteristics at least in part based on a type of process used for developing the TBC and affected by operational thermal loads to which a TBC is exposed. In one embodiment, the method allows detecting micro-structural features in a TBC, wherein the detecting of the micro-structural features is based on energy transmitted through the TBC, such as may be performed with a micro-feature detection system  20 . The transmitted energy is processed to generate data representative of the micro-structural features, such as may be generated by a controller  26 . The data representative of the micro-structural features is processed (e.g., by a processor  30 ) to determine at least one of the following: volumetric porosity information for the TBC and variation in the characteristics of the micro-structural features over a thickness of the TBC. Based on the results of the data processing, information is generated regarding at least one of the following: a present condition of the thermal barrier coating and a future likely condition of the thermal barrier coating. In another embodiment, one can estimate a level of thermal load to which the thermal barrier coating has been exposed.

RELATED APPLICATIONS

This application is related to patent application Ser. No. 11/242,664,titled “System and Computer Program Product For Non-DestructiveQuantification Of Thermal Barrier Coating Temperatures On Service RunParts”, filed concurrently with the present application, assigned incommon to the same assignee and herein incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The present invention is generally related to non-destructive inspectionof a thermal barrier coating (TBC), and, more particularly, to a systemand method for non-destructive quantification of TBC temperatures on aservice-run component.

BACKGROUND OF THE INVENTION

It is known to use various superalloy materials, such as cobalt ornickel-based superalloys, for making blades, vanes and other componentsfor power generating turbines, propulsion equipment, etc. These turbinescan operate at temperatures in the range of approximately 1000 Deg. C.to approximately 1700 Deg. C. and are generally protected by a series ofprotective coatings. The coatings may comprise layers of metallic basecoats, thermally grown oxide layers, as such layers grow in service-runcomponents and a final ceramic thermal barrier coating (“TBC”).Long-term exposure of these ceramic coatings to the hostile, hightemperature, abrasive environment in which such turbines typicallyoperate can cause phase destabilization, sintering, microcracking,delamination and ultimately spallation within the coating layers,exposing the superalloy component and possibly resulting in rapiddegradation or failure and potentially requiring costly and burdensomerepairs.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be more apparent from thefollowing description in view of the following drawings wherein:

FIG. 1 is a schematic representation of an exemplary system fornon-destructively inspecting and characterizing micro-structuralfeatures in a thermal barrier coating (TBC) on a component.

FIG. 2 shows exemplary sectional views along a thickness of a TBC as maybe generated with a micro-feature detection system based on X-raycomputed micro-tomography (XMT).

FIGS. 3A and 3B respectively illustrate three-dimensionalrepresentations of TBC microstructural features (e.g., pore morphologiesand cracks that may form in the TBC) as may be generated by a systemembodying aspects of the invention.

FIG. 4 is a plot as may be generated by a system embodying aspects ofthe present invention for quantifying changes in the microstructure(e.g., porosity) of a TBC with respect to exposure temperature of thecoating.

FIG. 5 is a graph that illustrates an exemplary functional relationshipthat may be used by a system embodying aspects of the present inventionfor correlating a measured micro-structural characteristic to estimate aTBC exposure temperature.

DETAILED DESCRIPTION OF THE INVENTION

Before describing in detail an exemplary system in accordance withaspects of the present invention, it should be observed that suchaspects reside primarily in a novel structural combination of amicro-feature detection system based on standard detection modalities,such as scattering/diffraction detection modalities, and computationalmodules configured to process data from such micro-feature detectionsystem and not necessarily in the specific modality of such a detectionsystem. Accordingly, the structure, control and arrangement of thedetection system have been illustrated in the drawings by readilyunderstandable block diagrams which show just those specific detailsthat are considered pertinent to the present invention, so as not toburden the disclosure with superfluous details that will be readilyapparent to those skilled in the art having the benefit of thedescription herein. Thus, any block diagram illustrations may notnecessarily represent each and every structural nuance, but areprimarily intended to generically illustrate the major components of thesystem in a convenient functional grouping, whereby aspects of thepresent invention may be more readily understood.

Thermal barrier coatings (TBCs) can be deposited onto blades, vanes andother components for power generating turbines, propulsion equipment,etc., using processes such as air plasma spraying (APS), electron beamphysical vapor deposition, (EB PVD) or chemical vapor deposition (CVD).These processes generally produce distinctive micro-structural featuresin the TBC for providing thermal protection to the component. Forexample, in APS TBC, the deposit is developed by successive impingementand inter-bonding of a plurality of splats that result in a layeredporosity predominantly parallel to the substrate where the TBC isdeposited. By way of comparison, TBCs produced by EB-PVD have a columnarmicrostructure with elongated intercolumnar pores predominantlyperpendicular to the substrate. Regardless of the specific process usedfor depositing the TBC, the coating can deteriorate and eventually failwhen, for example, the TBC surface is exposed over a relatively longperiod of time to temperatures that exceed a specified design limit ofthe coating.

The inventors of the present invention have recognized aTBC-characterizing technique that among other innovative aspects allowsestimating temperature exposure of in-service TBC components. Thisinvolves a determination of the micro-structural features of the TBCacross a thickness of the TBC. For example, a determination of porosityvariation across the TBC thickness may be made by generating datarepresentative of such micro-structural features.

FIG. 1 is a schematic representation of a system 10 fornon-destructively characterizing micro-structural features in a thermalbarrier coating on a component 12. The micro-structural features definepores and micro-cracks that can develop in the thermal barrier coating.The micro-structural features have characteristics at least in partbased on the type of process (e.g., APS or EB PVD) used for developingthe thermal barrier coating.

In one exemplary embodiment, system 10 includes a micro-featuredetection system 20 configured to detect the micro-structural featuresin the thermal barrier coating. The detection of the micro-structuralfeatures is based on energy transmitted through the coating. Forexample, in a detection system based on X-ray computed micro-tomography(XMT), such as may be used for 3-D imaging, an x-ray beam from an x-raysource 22 traverses the component 12, and the transmitted beam isincident on a detector 24, e.g., an array detector. The detection system20 includes a controller 26 connected to detector 24 to acquire andprocess data representative of the micro-structural features. It will beappreciated that other scattering/diffraction modalities for detectingmicro-features, such as Small-Angle Neutron Scattering (SANS), andUltra-Small-Angle X-ray Scattering (USAXS), may be employed providedthey are configured with sufficient energy and with the capability forextracting sufficient geometric information for non-destructivelyquantifying and/or visualizing the micro-structural features of the TBCon turbine parts. For readers desirous of obtaining general backgroundinformation in connection with various modalities experimentally usedfor conducting high-energy scattering/diffraction techniques on TBCs,reference is made to a dissertation presented on December 2002 by AnandA. Kulkarni to the Graduate School of the State University of New Yorkat Stony Brook, which dissertation is herein incorporated by referencein its entirety.

System 10 further includes a processor 30 configured to process the datarepresentative of the micro-structural features to determine in oneexemplary embodiment a volumetric porosity of the TBC and, in othercases, the variation in the characteristics of the micro-structuralfeatures over a thickness of the thermal barrier coating, or both. Inone exemplary embodiment, processor 30 includes an imaging module 32configured to form a three-dimensional image of the micro-structuralfeatures. The three-dimensional image is configured (e.g., withsufficient resolution) to enable a user to visually assess thevolumetric porosity of the TBC and/or the variation in thecharacteristics of the micro-structural features over the thickness ofthe thermal barrier coating. FIGS. 3A and 3B illustrate exemplary 3Dimaging representations of pore structures as may be generated byimaging module 32 to be displayed, for example, by a suitable userinterface 33.

Processor 30 may further include a quantitative information module 34configured to quantitatively assess the volumetric porosity of the TBCand/or the variation in the characteristics of the micro-structuralfeatures over the thickness of the thermal barrier coating. FIG. 4illustrates an exemplary plot as may be generated by quantitativeinformation module 34 for quantifying changes in the microstructure(porosity) of TBC coatings with respect to a level of temperatureexposure.

A module 36 may be configured to estimate a level of thermal load towhich the thermal barrier coating has been exposed. This estimate may bebased on the variation in the characteristics of the micro-structuralfeatures. Module 36 may be further configured to estimate time durationof exposure to the estimated level of thermal load. For example, thevariation in the characteristics of the micro-structural features may bemore pronounced the longer the duration of exposure to a given level ofthermal load.

A remaining life estimator module 38 may be configured for estimatingremaining life for a thermal barrier coating having been exposed to agiven level of thermal load. In one exemplary embodiment a storagedevice 40 may be provided for storing representative data of a virgincoating. In this embodiment, module 38 may be configured to relate datarepresentative of a TBC having been exposed to a given level of thermalload relative to the data representative of the virgin coating in orderto make an estimate of the remaining life for the TBC.

FIG. 2 shows exemplary graphical results obtained with a detectionsystem based on X-ray computed micro-tomography (XMT). Moreparticularly, FIG. 2 illustrates four reconstructed sectional images A,B, C and D of corresponding individual slices (as represented by linesA, B, C and D) along the thickness of a TBC specimen as shown in a graph50 obtained with a Scanning Electron Microscope (SEM). It will beappreciated that the reconstructed sectional images A, B and C showexemplary variation in intercolumnar spacing as a function of thickness,and more specifically show the intercolumnar spacing to be increasingtowards the top of the coating. Sectional image D essentially shows thetip of the columns.

FIGS. 3A and 3B illustrate exemplary TBC microstructural features (e.g.,pore morphologies) in respective 3D representations, wherein FIG. 3Aillustrates columnar pore structures in a TBC deposited by electron beamphysical vapor deposition (EB PVD), and FIG. 3B illustrates globularpore structures in a TBC deposited by air plasma spraying (APS). By wayof example and not of limitation, a dimension indicated by line L₂ mayrange from about 200 μm to about 250 μm in the TBC volume beinginspected.

FIG. 4 is a plot for quantifying changes that may occur in themicrostructure (porosity) of TBCs with respect to exposure temperature.It was observed that significant micro-structural changes can occur inthe TBCs upon exposure to increasing temperatures. This may be due toincreased sintering kinetics/diffusion. It was also observed thatsintering/column bridging leads to reduction of porosity and in turn toloss of strain tolerance. It was noted during experimental results theformation of regions of low porosity in the heat-treated coatings,indicating regions of column bridging/necking. These results showdecreasing porosity with increasing temperatures, consistent with highermeasured elastic modulus.

In operation quantitative analysis regarding porosity information,(e.g., volumetric porosity in the coating, and/or porosity gradientversus thickness) may be performed for as-deposited (virgin TBCcoatings) and aged TBC coatings by monitoring micro-structural changesthat develop over time due to operational-encountered heating. FIG. 5 isa graph that illustrates an exemplary functional relationship that maybe used for correlating a measured micro-structural characteristic(e.g., volumetric porosity in a particular section of the coating orlocal porosity at a given TBC thickness) to a TBC exposure temperature.This may be useful to determine a thermal gradient across the TBC,which, for example, may indicate a local heat flux to which thecomponent has been subjected, as opposed to a flux value derived from atheoretical thermal model. It will be appreciated that this wouldprovide valuable information to a component designer. For example, thismay allow the designer to better map the heat loads that the componentactually has to withstand in operation. This may be used for validatingor updating the thermal model used by the designer to predict the heatflux at a given component location. Moreover, aspects of the presentinvention may be used for estimating TBC surface temperatures ofservice-run parts. It is contemplated that this capability will beconducive to more consistently and more accurately identifying the roleof TBC over-temperature conditions as a cause of TBC degradation thatcould ultimately lead to spallation of the TBC.

Aspects of the invention can also be embodied as computer readable codeon a computer readable medium. The computer readable medium is any datastorage device that can store data, which thereafter can be read by acomputer system. Examples of computer readable medium include read-onlymemory, random-access memory, CD-ROMs, DVDs, magnetic tape, optical datastorage devices. The computer readable medium can also be distributedover network coupled computer systems so that the computer readable codeis stored and executed in a distributed fashion.

Based on the foregoing specification, the invention may be implementedusing computer programming or engineering techniques including computersoftware, firmware, hardware or any combination or subset thereof. Anysuch resulting program, having computer-readable code means, may beembodied or provided within one or more computer-readable media, therebymaking a computer program product, i.e., an article of manufacture,according to the invention. The computer readable media may be, forexample, a fixed (hard) drive, diskette, optical disk, magnetic tape,semiconductor memory such as read-only memory (ROM), etc., or anytransmitting/receiving medium such as the Internet or othercommunication network or link. The article of manufacture containing thecomputer code may be made and/or used by executing the code directlyfrom one medium, by copying the code from one medium to another medium,or by transmitting the code over a network.

An apparatus for making, using or selling the invention may be one ormore processing systems including, but not limited to, a centralprocessing unit (CPU), memory, storage devices, communication links anddevices, servers, I/0 devices, or any sub-components of one or moreprocessing systems, including software, firmware, hardware or anycombination or subset thereof, which embody the invention as set forthin the claims.

User input may be received from the keyboard, mouse, pen, voice, touchscreen, or any other means by which a human can input data to acomputer, including through other programs such as application programs.

One skilled in the art of computer science will easily be able tocombine the software created as described with appropriate generalpurpose or special purpose computer hardware to create a computer systemor computer sub-system embodying the method of the invention.

While the preferred embodiments of the present invention have been shownand described herein, it will be obvious that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions will occur to those of skill in the art without departingfrom the invention herein. Accordingly, it is intended that theinvention be limited only by the spirit and scope of the appendedclaims.

1. A method for non-destructively inspecting and characterizingmicro-structural features in a thermal barrier coating on an in-servicecomponent of a power generating turbine, wherein said micro-structuralfeatures define pores and cracks, if any, in said thermal barriercoating, said micro-structural features having characteristics at leastin part based on a type of process used for developing said thermalbarrier coating and affected by thermal loads to which a thermal barriercoating is exposed during operation of the power generating turbine,said method comprising: selecting an in-service component of the powergenerating turbine to be monitored over a period of time; detectingmicro-structural features in a thermal barrier coating of the selectedin-service component, wherein the detecting of the micro-structuralfeatures is based on energy transmitted through said coating, whereinthe thermal barrier coating is expected to encounter heat flux valuesbased on a theoretical thermal model configured to map heat flux valuesfor a plurality of locations of the in-service component; processingsaid transmitted energy to generate data representative of saidmicro-structural features; processing the data representative of saidmicro-structural features to determine at least one of the following:volumetric porosity information for the thermal barrier coating andinformation regarding variation in the characteristics of saidmicro-structural features over a thickness of said thermal barriercoating; based on the results of said data processing, generatinginformation regarding at least one of the following: a present conditionof the thermal barrier coating and a future likely condition of thethermal barrier coating; generating an image indicative of theinformation regarding the present condition of the thermal barriercoating and/or the future likely condition of the thermal barriercoating; validating with the information indicated by the generatedimage whether heat flux values based on the theoretical thermal modelcorrespond to actual heat flux values encountered by the in-servicecomponent during operation of the power generating turbine; based on theactual heat flux values encountered by the in-service component,estimating a remaining operational life of the thermal barrier coating,said estimating further comprising relating representative data of thethermal barrier coating having been exposed to thermal loads relative torepresentative data of a virgin coating; and generating a representationindicative of the remaining operational life of the thermal barriercoating.
 2. The method of claim 1 wherein the detecting comprisesperforming a computerized micro-tomography scan of the thermal barriercoating, and the representative data comprises three-dimensional data ofsaid micro-structural features based on the computerizedmicro-tomography scan.
 3. The method of claim 2 further comprisingprocessing said three-dimensional data to form a three-dimensional imageof said micro-structural features, configuring said three-dimensionalimage with sufficient resolution to enable a user to visually asses atleast one of the following: the volumetric porosity information and thevariation in the characteristics of said micro-structural features overthe thickness of said thermal barrier coating.
 4. The method of claim 2further comprising processing said three-dimensional data toquantitatively assess at least one of the following: the volumetricporosity information for said thermal barrier coating and the variationin the characteristics of said micro-structural features over thethickness of said thermal barrier coating.
 5. The method of claim 1wherein the detecting of the micro-structural features is selected fromthe group consisting of detecting based on computerized micro-tomographyscanning, detecting based on small angle neutron scattering, anddetecting based on ultra-small angle x-ray scattering.
 6. The method ofclaim 1 further comprising correlating the variation in thecharacteristics of said micro-structural features over the thickness ofsaid thermal barrier coating to a predefined model to estimate a levelof thermal load to which the thermal barrier coating has been exposed.7. The method of claim 6 further comprising estimating duration ofexposure to the estimated level of thermal load.
 8. The method of claim1 further comprising correlating the volumetric porosity information toa predefined model to estimate a level of thermal load to which thethermal barrier coating has been exposed.
 9. The method of claim 1wherein the type of process used for developing said thermal barriercoating is selected from the group consisting of a plasma sprayedprocess, an electron beam physical vapor deposition process and achemical vapor deposition process.
 10. A method for non-destructivelyinspecting and characterizing micro-structural features in a thermalbarrier coating on an in-service component of a power generatingturbine, wherein said micro-structural features define pores and cracks,if any, in said thermal barrier coating, and said micro-structuralfeatures have characteristics at least in part based on a type ofprocess used for developing said thermal barrier coating and affected byoperational thermal loads to which a thermal barrier coating is exposedduring operation of the power generating turbine, said methodcomprising: selecting an in-service component of the power generatingturbine to be monitored over a period of time; detectingmicro-structural features in a thermal barrier coating of the selectedin-service component, wherein the detecting of the micro-structuralfeatures is based on energy transmitted through said coating, whereinthe thermal barrier coating is expected to encounter heat flux valuesbased on a theoretical thermal model configured to map heat flux valuesfor a plurality of locations of the in-service component; processingsaid transmitted energy to generate data representative of saidmicro-structural features; processing the data representative of saidmircro-structural features to determine at least one of the following:volumetric porosity information for the thermal barrier coating, andinformation regarding variation in the characteristics of saidmicro-structural features over a thickness of said thermal barriercoating; based on the results of said data processing, estimating alevel of thermal load to which the thermal barrier coating has beenexposed; generating a signal indicative of the information regarding thelevel of thermal load to which the thermal barrier coating has beenexposed; validating with the information indicated by the generatedsignal whether heat flux values based on the theoretical thermal modelcorrespond to actual heat flux values encountered by the in-servicecomponent during operation of the power generating turbine; based on theactual heat flux values encountered by the in-service component,estimating a remaining operational life of the thermal barier coating,said estimating further comprising relating representative data of thethermal barrier coating having been exposed to thermal loads relative torepresentative data of a virgin coating; and generating a representationindicative of the remaining operational life of the thermal barriercoating.
 11. the method of claim 10 further comprising estimating timeduration of exposure to the estimated level of thermal load.
 12. Themethod of claim 10 wherein the estimating of the level of thermal loadto which the thermal barrier coating has been exposed comprisescorrelating the variation in the characteristics of saidmicro-structural features over the thickness of said thermal barriercoating to a predefined model.
 13. The method of claim 10 wherein theestimating of the level of thermal load to which the thermal barriercoating has been exposed comprises correlating the volumetric porosityinformation to a predefined model.
 14. The method of claim 10 whereinthe detecting comprises performing a computerized micro-tomography scanof the coating, and the representative data comprises three-dimensionaldata of said micro-structural features.
 15. The method of claim 14further comprising processing said three-dimensional data to form athree-dimensional image of said micro-structural features, configuringsaid three-dimensional image with sufficient resolution to enable a userto visually assess at least one of the following: the volumetricporosity information for said thermal barrier coating and the variationin the characteristics of said micro-structural features over thethickness of said thermal barrier coating.
 16. The method of claim 14further comprising processing said three-dimensional data toquantitatively assess at least one of the following: the volumetricporosity information for said thermal barrier coating and the variationin the characteristics of said micro-structural features over thethickness of said thermal barrier coating.
 17. The method of claim 10wherein the detecting of the micro-structural features is selected fromthe group consisting of detecting based on computerizedmicro-tomography, detecting based on small angle neutron scattering, anddetecting based on ultra-small angle x-ray scattering.
 18. the method ofclaim 10 wherein the type of process used for developing said thermalbarrier coating is selected from the group consisting of a plasmasprayed process and physical and chemical vapor deposition process.